The present invention relates to dimmable ballast systems.
In existing ballast circuits for powering fluorescent lamps at an adjustable illumination level, a number of different methods are used for dimming control. One popular method for dimming control employs a phase-control device, such as a triac. The phase-control device is used to modify a firing phase angle of an alternating current (AC) powering signal. A dimming ballast circuit, in turn, controllably dims a fluorescent lamp based on the firing phase angle.
Another popular method for dimming control is based on a direct current (DC) input, such as a 0 to 10 Volt DC input, distinct from an AC powering signal. In this method, an inverter circuit controllably dims a fluorescent lamp based on the magnitude of the DC input.